The effects of suspended sediments on the composition of wall communities in Alaskan fjords were investigated by quantitative assessment of underwater photo-quadrats. In fjords with actively retreating tidewater glaciers, suspended sediment levels were extremely high at the heads and were exponentially lower at the mouths. Fjords without glaciers had low suspended sediment levels throughout. The per cent cover and number of species were lowest where sedimentation was highest, at the heads of glacial fjords. Here the wall communities were dominated by a sparse cover of small serpulid worms. Richer communities comprising mostly algae, sponges, hydroids, bryozoans, tunicates and brachiopods were found in fjords without glaciers, and at the mouths of glacial fjords. There was a positive correlation between water clarity and community composition along a gradient from heads to the mouths of fjords with high suspended sediment levels., Cited By (since 1996):3, Invertebrates,
Ecology, CODEN: POBID, ,

A framework for investigating general patterns of benthic β-diversity along estuaries

Description

The description of major patterns in beta (. β) diversity is important in order to understand changes in community composition and/or richness at different spatial and temporal scales, and can interrogate processes driving species distribution and community dynamics. Human impacts have pushed many estuarine systems far from their historical baseline of rich, diverse, and productive ecosystems. Despite the ecological and social importance of estuaries, there has not yet been an attempt to investigate patterns of β-diversity and its partitioning along estuarine systems of different continents. We aimed to evaluate if benthic assemblages would show higher turnover than nestedness in tropical than in temperate systems, if well-known impacted estuaries would show greater nestedness than less polluted systems, and to propose a conceptual framework for studying benthic macrofauna beta diversity along estuaries. We analyzed subtidal benthic macrofaunal data from estuaries in Brazil, USA and France. We estimated alpha (. α), beta (. β) and gamma (. γ) diversity for each sampling time in each system, investigated patterns of β -diversity as multivariate dispersion and the partitioning (nestedness and replacement) of β-diversity along each estuary. There was a decrease in the α-diversity along marine to freshwater conditions at most of the estuaries and sampling dates. Beta diversity as multivariate dispersion showed high variability. Most of the estuaries showed a greater proportion of the β-diversity driven by replacement than nestedness. We suggest a conceptual framework for estuaries where relatively pristine estuaries would have their β-diversity mostly driven by replacement while impacted estuaries subjected to several anthropogenic stressors would show total nestedness or total replacement, depending on the stress.

Cited By (since 1996):61, CODEN: MPNBA, Benthic sediments and animals are highly modified by human activities at McMurdo Station, the largest human settlement in Antarctica. The quantity of anthropogenic debris, contamination of marine sediments with hydrocarbons and metals, and gross changes in benthic communities are largely confined to Winter Quarters Bay, adjacent to the former dump site and the ice dock used by visiting ships. Levels of purgeable hydrocarbons in bay sediments are as high as 4500 ppm. Metal levels are mostly high within the bay, but are not greater than in the most polluted temperate habitats. Levels of anthropogenic chemicals are significantly higher in the back bay compared to stations established at different distances from the bay (along three potential contamination gradients), including reference sites many kilometres away. There are significant negative correlations between the total number of infauna or epifauna and the concentrations of hydrocarbons and most metals in sediments. The few animals living in the back bay are motile polychaete worms with opportunistic life histories, primarily Capitella capitata antarcticum and Ophryotrocha claparedii. Fortunately, the local physical setting apparently permits little transport of contaminated sediments from the bay, which is flanked on one side by a large submarine ridge and on the other by Hut Point. Hut Point also protects the bay from oceanic conditions. The back bay is over 30 m deep and the ridge top is only 18 m deep. The gradient of chemical and community change is extremely steep, but there are observable ecological impacts outside the bay along the front of the station. Although most historical inputs of pollution are removed or reduced and continued cleanup is planned, Winter Quarters Bay may require many decades to recover., ,

Swarming benthic crustaceans in the Bering and Chukchi seas and their relation to geographic patterns in gray whale feeding,

Description

Swarms differed in their geographic extent, local biomass, and life stages of swarming individuals and thus in their availability to feeding Eschrichtius robustus. Immature amphipods apparently swarmed for dispersal, whereas cumaceans probably swarmed for mating. All life stages of the hyperbenthic mysids occurred above the sea floor. Although the geographic spread of mysid swarms and shrimp communities was much greater than for the amphipod and cumacean swarms, the latter swarmed in denser patches to produce higher local biomass. Crustacean swarms are important in describing the geographic patterns of gray whale feeding from the Chukchi Sea to Baja California. The primary feeding ground is in the S Chukchi Sea and especially the N Bering Sea, where gray whales suck infaunal amphipods from fine sand. The primary feeding ground is divided into a relatively deep zone (>20 m), where tube-dwelling ampeliscid amphipods are the major prey, and a shallow zone (<20 m), where burrowing pontoporeid amphipods dominate. The secondary feeding ground is in the S Bering Sea along the E Alaska Peninsula and adjacent Alaskan mainland where shrimp and mysids are the major prey. -from Authors, Cited By (since 1996):16, Invertebrates,
Marine Mammals, Birds & Turtles, ,

High species density patterns in macrofaunal invertebrate communities in the marine benthos,

Description

Species density of macrofaunal invertebrates living in marine soft sediments was highest at the shelf-slope break (100-150m) in Monterey Bay (449 m-2). There were 337 species m-2 in the mid-shelf mud zone (80 m). There were fewer species along the slope: 205 m-2 from the lower slope (950-2000 m) and 335 m-2 on the upper slope (250-750 m). Species density was highest inside the bay (328-446 m-2) compared to outside (336-339 m-2), when examining samples at selected water depths (60-1000 m). There was little difference in local species density from 1 km of shoreline compared to regional species density along 1000 km of shoreline at both shelf and slope depths. The highest species densities worldwide in the literature are recorded along the Carolina slope in the Atlantic Ocean, where peak species density (436/0.81 m2) at 800 m and values at the largest sample areas are similar to those on the Monterey Bay shelf. We speculate that the highest species densities occur where ocean water exchanges energy with shoaling topography at the continental margin, bringing more food to the benthos -- areas such as the very productive waters in the upwelling system of Monterey Bay., Cited By (since 1996):1, ,

Destruction and opportunity on the sea floor: effects of gray whale feeding,

Description

Eschrichtius robustus are highly disruptive bottom feeders that remove infaunal invertebrate prey and sediments by suction. The response of the benthos to gray whale feeding was examined in the primary feeding grounds of the Bering Sea and in an ecological analog of these prey communities along the W coast of Vancouver Island. Large feeding excavations (often 2-20m2) were rapidly colonized by scavenging lysianassid amphipods, especially Anonyx spp. that attacked injured and dislodged infauna. Many of the attacked animals were small crustaceans (<1cm long) and polychaete worms. Anonyx spp. was 20-30 times more abundant inside fresh excavations than in the surrounding tube mat, where they dispersed within hours after the initial feeding disturbance. A smaller species of lysianassid, Orchomene minuta, invaded less rapidly and remained much longer in excavations than the larger, Anonyx spp. Within days and weeks, gray whale feeding excavations trapped organic debris. Most invading species were much more abundant in debris patches compared to debris-free areas of the same excavations. The numbers of some colonists remained elevated in disturbed areas for 2 mo., Cited By (since 1996):68, ,

Ice scour disturbance to benthic communities in the Canadian High Arctic,

Description

Seabed scouring by ice is a large-scale disturbance to polar coasts. Grounding ice modifies seabed topography, reworks the sediment, and ploughs and crushes the seabed biota. The effects of ice scour on soft-sediment benthos were examined in Barrow Strait in High Arctic Canada. Due to the variability of ice keel depths in this area, the Barrow Strait coast was found to exhibit a gradient of ice scour disturbance to 30 m depth. The inshore shallows were highly scoured by the abundant shallow draft ice. Deeper water scours caused by icebergs and portions of ice shelves were less frequent. The benthos paralleled this disturbance gradient, with the inshore consisting of a disturbance-associated fauna. Four recently formed ice scours were studied at 3 locations. Despite differences in exposure to currents and water depth, all scours were dominated by the same disturbance-associated fauna and were distinctive from the benthos outside. Scavenging amphipods and gastropods consumed bivalves that were dislodged and damaged, while predatory amphipods and opportunistic polychaetes burrowed in the gouged and displaced clays. Our expectation was that the topography of the ice scours would select for different colonizing species. However, there was no evidence of preferential occupation of the raised berms by suspension feeders or of the troughs by deposit feeders. The species that dominated the 4 scours also dominated the less recently disturbed areas of the inshore, despite the fact that these areas were situated 300 to 400 m inshore and at shallower depth. The prevalence of species that associate with ice scours indicates that ice disturbance is an important factor that molds coastal benthic zonation at this Arctic location., Cited By (since 1996):65, CODEN: MESED, , , Downloaded from: www.int-res.com/articles/meps/166/m166p001.pdf (9 June 2014).,

Cited By (since 1996):15, Invertebrates, CODEN: MBIOA, The two species of infaunal amphipod crustaceans Rhepoxynius abronius (Phoxocephalidae) and Eohaustorius sencillus (Haustoriidae) are characteristic of nearshore sandy bottoms along the California (USA) coast, and are highly sensitive to moderate levels of heavy metals. In laboratory experiments, both zinc and the chelator EDTA increased the survival of amphipods in sediment containing otherwise lethal levels of cadmium (8.5 ug g-1), which are representative of moderately polluted environments. In simple choice experiments, amphipods prefer sediment with complexed cadmium. The behavioral and survival patterns of both species were similar in the experiments. EDTA prevented about 50% of the added cadmium from initially being incorporated into the sediment, and increased the rate of cadmium released from the sediment. These data illustrate the limitation of operational definitions of chemical analyses, since weak-acid (0.5 N HCl) leaches that were intended to provide an estimate of the "biologically available" metal concentrations extracted both toxic and EDTA-complexed cadmium species and did not account for their antagonistic interactions with zinc., ,